Introduction

Cryotherapy involves the destruction of tissues by extreme cold (Box 24-1). The tissue is frozen to subzero temperatures, which is then followed by sloughing of dead tissue. Several mechanisms are involved including the osmotic effects of intracellular water leaving the cell and causing dehydration, intracellular ice formation disrupting the cell membrane and ischaemic damage due to freezing of vessels. Liquid nitrogen is most commonly employed, although various freezing agents are available such as solid carbon dioxide, nitrous oxide, and a mixture of dimethyl ether and propane. Unless otherwise stated, the rest of this section relates to liquid nitrogen cryotherapy.

The low temperature of liquid nitrogen (–196 °C), ease of storage and relative low cost make it an effective and convenient cryogen. However, its low temperature also results in rapid evaporation and therefore it should be stored carefully in an adequately ventilated area and preferably in a pressurised container.

Application technique

The liquid nitrogen is best applied as a spray using a canister (Figure 24-1).

An alternative method is to use a cotton bud that is immersed in liquid nitrogen and then applied to the lesion being treated, using moderate pressure until frozen. More than one application may be needed. A fresh cotton bud should be used for each patient to diminish the risk of transferring human papillomavirus. However, with this method there in an increase in temperature partly due to poor thermal capacity of the cotton and also warming when the cotton tip is transferred from the liquid nitrogen container to the patient's skin. The freeze time is important and will vary according to the lesion being treated.

Freeze time is counted from the moment the entire lesion becomes frozen white rather than simply from when spraying begins. Once spraying is complete, the rate of thawing of the tissue is a crucial factor as more tissue destruction occurs with rapid freezing and slow thawing. The 'freeze-thaw' cycle may be repeated to increase the degree of damage and the additional freeze has a greater penetration due to improved cold conductivity of the previously frozen tissue. Freeze times and the number of freeze-thaw cycles depend on the type of lesion (i.e. whether benign or malignant) as well as the size and thickness.

Risks and precautions

• Patients should be warned about reactions which can occur within the first 48 hours after treatment such as pain, redness, swelling, and blistering, so that they are not unduly alarmed. A potent topical steroid cream applied over the affected area for a few days can be used to limit this.
• Ulceration may occur, particularly on the lower limb if there is poor perfusion.
• Although secondary bacterial infection is rare, increased pain, redness or swelling after two to three days may be indicative of this.
• Later risks include scarring and, particularly in darker skin types, hypopigmentation, or hyperpigmentation. As would be expected, these are more of an issue with prolonged treatments.

Skin lesions suitable for freezing

Cryotherapy is usually initiated based on a clinical diagnosis without prior histological confirmation, and therefore, the clinician must be confident of the diagnosis. If there is any diagnostic doubt, consider a biopsy first or alternative treatment modality where histology can also be obtained. The following lesions are frequently treated with cryotherapy.

Viral warts

A single freeze lasting 10-30 seconds per treatment, which includes a 1-2 mm margin of normal skin, is often sufficient, although a double freeze-thaw cycle may improve clearance, particularly for thicker warts. Usually several treatments at two- to three-week intervals are necessary, and cryotherapy may be combined with topical therapies such as salicylic acid preparations for increased efficacy. Paring down the wart with a blade before cryotherapy can also be helpful.

Seborrhoeic keratoses

A single freeze of between 5 and 20 seconds including a 1- to 2-mm margin of normal skin should be effective for most lesions. A frozen lesion once thawed for a few seconds can also be curetted off. Larger, thicker lesions may require prolonged freezing or repeat freeze-thaw cycles, thereby increasing pain and inflammation. In these circumstances, it may be better to curette and gently cauterise the area.

Papillomas and skin tags

A single freeze of 5-10 seconds may be sufficient, and it is helpful to stabilise the skin tag with metal forceps so that the liquid nitrogen is sprayed obliquely, avoiding non-lesional skin. An alternative method is to treat by compression with artery forceps dipped in liquid nitrogen.

Actinic keratosis

A single freeze of between 5 and 15 seconds including a 1- to 2-mm margin of normal skin is advised. When necessary, lifting away hard keratin to expose the underlying abnormal epithelium makes the freezing more effective. Rarely, a double freeze-thaw cycle may be needed but be aware that a lesion which does not respond to cryotherapy may be a squamous cell carcinoma.

Bowen's disease

This is an intraepidermal (in situ) form of squamous cell carcinoma, which can be effectively treated with a single freeze of up to 30 seconds including a 1- to 2-mm margin of normal skin. Again, a biopsy is necessary should there be any doubt about the diagnosis, and follow-up is essential to make sure the lesion has cleared and is not progressing.

Basal cell carcinoma

If cryotherapy is to be employed, it is best limited to the treatment of the superficial type of basal cell carcinoma (BCC), when lesions are primary (i.e. previously untreated), small (1 cm in diameter) and well defined. The cure rate for other types of BCC is inferior with cryotherapy than with other forms of treatment such as excision. Two cycles of freezing lasting between 20 and 30 seconds, including a 3-mm rim of clinically normal skin, with a thaw time of 2 minutes is often effective.

Electrosurgery

This term describes the use of electricity to cause thermal tissue destruction. There are two main forms of treatment: electrocautery and electrodessication.

Electrocautery

Heat from an electrically heated element causes thermal damage by direct transfer of heat. Remember that in this situation, the treating element is hot.

Electrodessication (diathermy or hyfrecation)

High frequency alternating current energy is converted to heat because of tissue resistance. The treatment electrode is cold as heat generation occurs within the tissue. Electrode contact with skin causes superficial tissue dehydration. A variation of electrodessication is electrofulguration in which the electrode is held 1-2 mm from the skin surface to cause superficial epidermal carbonisation. Furthermore, depending on the voltage of current used and electromagnetic waveform, the degree of tissue cutting (electro-section) and coagulation (electrocoagulation) can be modified. If only one treatment electrode is present, then alternating current variably enters and exits the tissue, with electrons being randomly dissipated into the environment, and this is known as a monopolar procedure. However, if there is also a second indifferent electrode that completes an electrical circuit, the procedure is termed bipolar. With alternating current, the treatment electrodes are not truly positive or negative poles, and the terms mono- and biterminal are more accurate.

In routine dermatology, electrocautery or electrodessication can be used as the sole treatment for vascular lesions such as spider naevi and telangiectasia, although a vascular laser may produce better results with a lower risk of scarring. However, it is more commonly used for haemostasis during skin surgery (Figure 24-2) or in combination with curettage (see below).

Curettage

This is a simple method of removing superficial lesions, particularly in areas with thick underlying dermis such as the trunk and extremities (Box 24-2). A metal spoon or ring with a sharp edge is used to scrape away the lesion (Figure 24-3a,b). The advantage over cryotherapy is that a sample can be sent for histology, although completeness of removal cannot be accurately assessed. Curettage is combined with electrodessication or electrocautery to treat benign lesions such as seborrhoeic keratoses and xanthelasma as well as dysplastic lesions (actinic keratoses and Bowen's disease) and BCC. For curettage to work well, the lesion ideally should be softer than the surrounding unaffected skin.

Lesions suitable for curetting include

• seborrhoeic keratoses
• solitary viral warts
• actinic keratoses and Bowen's disease
• cutaneous horns
• small BCCs.

Technique

The area under and around the lesion is injected with a local anaesthetic. Next, using the thumb and index finger of the non-dominant hand ensure that the skin around the lesion is taut, so that there is a firm base on which to curette. Curette off the lesion and then cauterise the base to achieve haemostasis as well as to destroy any remaining tumour. Avoid curetting normal skin. For BCCs, the process is repeated so that a total of two or three cycles of curettage and electrocautery/electrodessication is performed.

Risks and precautions

• Patients should be warned that the wound may take three to four weeks to heal and that although the resultant scar will hopefully be a flat, white patch, it could ultimately become indented (atrophic) or even be pink and raised (hypertrophic), especially with more aggressive treatment causing a deep wound.
• Ulceration may occur, particularly on the lower limb if there is poor perfusion.
• The types of BCCs best treated with this method are primary, nodular, small (1 cm diameter), well defined and in non-high risk or cosmetically sensitive sites. Sites generally to be avoided include the area around the eyes, nose, lips, chin, ears, and hair-bearing scalp.
• If curettage results in exposure of subcutaneous fat, then the procedure should be abandoned, and the area excised down to fat and usually sutured. This is because firstly it is not possible to distinguish accurately between soft tumour and fat, and secondly the outcome will be suboptimal in terms of wound healing and scarring, once the fat layer has been breached.

Diagnostic biopsies

Although in many circumstances a diagnosis can be confidently made on clinical examination alone, often it is important to secure a diagnosis with the aid of histopathology. For example, a melanocytic naevus may be proved on histology to be completely benign or, by complete contrast, a malignant melanoma. There are different methods of performing a diagnostic biopsy, each with its own advantages and disadvantages. The area to be biopsied must be adequately infiltrated with local anaesthesia before commencing the procedure.

Shave biopsy

This is appropriate for sampling or removing lesions which are limited to the epidermis and papillary dermis including seborrhoeic keratoses, nodular BCCs, and naevi. The skin is held taut and the lesion is gently sliced with either a scalpel blade or double-edged razor blade held horizontal to the skin surface. The angle of the blade controls the depth, but the aim should be to reach the mid-dermis. Haemostasis can be achieved with electrosurgery or aluminium chloride but firm pressure may suffice. One advantage of this technique is that sutures are unnecessary. However, this technique is not recommended for any suspicious naevus, which should be excised entirely.

Punch biopsy

The biopsy tool comes in sizes varying from 2 to 8 mm (Figure 24-4) and consists of a small cylinder with a cutting rim which is used to penetrate the epidermis by rotation between the operator's finger and thumb. The skin is held taut at 90° to the orientation of the relaxed skin tension lines ('wrinkle lines') so that an oval defect results, which is easier to close (Figures 24-5 24-6 24-7 24-8 24-9). The resulting plug of skin is lifted out with forceps and cut off as deeply as possible. Pressure and/or electrosurgery is required for haemostasis. The advantage over a shave biopsy is that the specimen obtained is of full thickness containing epidermis, dermis, and fat, but the area sampled is smaller. The punch biopsy tool can also be used to make holes over cysts and lipomas through which the contents can be extruded. Usually the defect left by the punch is sutured, although for smaller sizes (2 or 3 mm) secondary intention healing might be considered depending on the site.

Incisional biopsy

This is suitable for larger lesions and is taken across the margin of the lesion in the form of an ellipse. It is essential to include deeper dermis in certain conditions; for example, granuloma, or lymphoid infiltrate may not be near the surface. An adequate amount of normal tissue should be included, so that this can be compared with the pathological area and this also means there is enough normal skin to suture the incision together (Figure 24-10).

Surgical excision

Excision of skin lesions is both curative and diagnostic. It may be the best way of making a diagnosis if there are multiple small papules or vesicles, one of which can be excised intact. Incisions should follow tension or wrinkle lines (Figures 24-11 24-12 24-13 ).

In the case of malignant lesions, it is particularly important that the whole lesion is adequately excised. The pathologist can report on the adequacy of excision, but this is hard to assess in lesions such as multifocal BCC where there are scattered collections of cells. If there is likely to be any doubt about the excision being complete, it is helpful to attach a suture to one end of the excised specimen so that the pathologist can describe which border, if any, extends over the excision margin.

Technique

The basic technique consists of making an elliptical incision (Figures 24-14 24-15 24-16 ) with the length three times the width and the angles at the poles about 30° to minimise the formation of standing cones of tissue, also known as dog ears. The long axis of the excision should be parallel to the 'wrinkle lines' of the skin or to the Langer lines. Although on most parts of the body these correspond closely, they are not exactly the same, as Langer lines correspond to the alignment of collagen fibres within the dermis. Scars parallel to these tend to heal better and be less obvious. Lesions excised on the sternal area, upper chest, and shoulders are more likely to result in keloid scar formation and may be best referred to a dermatological or plastic surgeon.

Local anaesthetic is injected subcutaneously but close to the skin. The incision should be vertical rather than wedge shaped. Before suturing (Box 24-4) of the wound, undermining is often required to reduce wound tension. This involves dissection of the skin subdermally (blunt and/or sharp), although the depth will depend on the body site.

Where a wound cannot be closed directly (i.e. from side to side) or if direct closure does not produce the best aesthetic outcome then a cutaneous flap or skin graft may be appropriate. Flaps may be advancement, rotation, or transposition. Grafts are defined as full thickness if the entire epidermis and dermis is included, and split thickness if less than the entire dermis is included. These are outside the scope of this book.

Mohs micrographic surgery

For certain higher risk tumours (most commonly BCC and squamous cell carcinoma) Mohs micrographic surgery is the treatment of choice. Factors which determine a higher risk may include aggressive histology, ill-defined margins, large size (>2 cm), critical site such as eyes, lips, nose, and ears and recurrence following previous treatment. Unlike standard excision with pre-determined margins, the tumour is debulked and excised with a narrow clinical margin. The tissue is labelled with different coloured inks and mapped to the wound on the patient. In standard Mohs practice, the tissue is then processed for microscopic examination with frozen sections usually within one hour. Specially trained Mohs biomedical scientists and processing equipment are required in close proximity to the operating room/theatre. The sections in Mohs surgery are horizontal and therefore the entire margin is visualised as compared with conventional excision when they are vertical (like bread loaf slices) so that only a small percentage is analysed. The Mohs surgeon reads the slides and if tumour is still present within the tissue sections, takes more tissue precisely where it is still evident on the patient. This ensures that the tumour resection involves the least amount of normal tissue and yet achieves the highest likelihood of cure.